Wide band amplifier



April 2l, 1942. D. E. NQRGAARD WIDE BANP AMPLIFIER Fiied May 1, 1941gaard, M4

Patented Apr. 21, 1942- WIDEBANDAMPLTFIER. W Donald E. Norgaard,Schenectady, N. Y., assigner to General Electric Company, a corporationof New York Application May 1, 1941, Serial No. 391,318 12 Claims. (Ci.179-171) My invention relates to wide band amplifiers such as thoseemployed for the amplification of vrvideo frequency currents usedintelevision.

It has for one of its objects to provide a method and means forproducing, uniform amplification at all frequencies of such currentsfrom a level only slightly in excess of the undesired disturbing, ornoise, currents to substantially higher level notwithstanding 'theattenuating'eiects of such shunt capacitiesas are usually present,

In television transmitters, camera tubes are employed which are exposedto the scene to be televised and which produce currents representingsuch scene. This discharge device has very high impedance such that thecurrents owing therefrom are not materially affected by the loadimpedance into which the tube operates. These currents may havefrequencies extending over the range from zero to about ve megacycles.An object of my invention is toprovide improvedmeans method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description forproducing uniform amplication for these currents throughout thisfrequency range.

It so happens, in the use of the camera tube, that the currents producedthereby most faithfully represent the televised scene if adjustedto beas small as possible; i. e., the smaller the currents the better theyrepresent the televised picture. Accordingly, one normally adjusts theelectron beam of the camera tube to as low intensity as possible andstill produce ampliilable output currents. Of course, the undesireddisturbing, or,

so called, noise, currents produced in the amplifier chain define thelower limit, it being necessary that the camera tube output currents beof intensity such that when amplified in the amplifier chain they havean intensity level sufciently above the undesired noise level. Theseundesired currents extend throughout the frequency band to betransmitted lbut the most objectionable of them are in the frequencyrange below two thousand cycles, or substantially below the linerepetition rate employed in the scanning process.

Difllcultyis amplification over the band of frequencies to be amplifiedbecause of the low level of the desired signal with respect to the noiselevel and because of the attenuating effects of shunt capacity in.-herently present throughout the amplifier.

An object of my invention is to overcome this difficulty and secureuniform amplication throughout the band while minimizing the effects ofdisturbing currents introduced by the amplit fier.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and encountered ineffecting uniform i taken in connection with the accompanying drawing,in which Fig. 1`rep'resents yan embodiment of my invention, and Fig;f2a, Fig. 2b, Fig. 2c and Fig. 2d represent-.certain characteristicspertaining to its operation.

Referring to Fig. 1 of the drawing,` I have shown therein anamplification channel extending from terminals I, 2 to terminals 3,. I.The terminals i, 2 may, of course, be connected tothe output terminalsof a. cathoderay. or camera, tube used in picking up the scene to beAtelevised and these terminals are connected to the input electrodes ofan amplifier represented by the rectangle AB. l.

Fig. 1 includes three rectangles E, 8 and 1, each of which may be` takento represent either a single stage electron discharge amplier oralmultistage amplier but in the usual case these rectangles represent amulti-stage ampliiier. Preferably the last stage in each of theseamplifiers is of the pentode type, such high internal output impedanceand produces output current which is independent of the magnitude of theload impedance.

The terminal l may be considered to be connected to the input grid thatit has extremely of such an amplifier and means as may be employed.Operating potential for the anodes of the discharge devices representedby the rectangles 5, 6, and `'I may be supplied through conductors 8, 9,and l0 respectively to the respective anodes -of the different dischargedevices.

The network Ii between rectangles 5 and is the interstage couplingnetwork connected between the anode and the cathode of the lastdischarge device represented by rectangle 5 and the grid and cathode ofthe first discharge device represented by rectangle 6.A Similarly, thenetwork i2 between rectangles 6 `and i represents the coupling networkconnected between the anode and cathode of the last discharge devicerepresented by rectangle 6 and the grid' and cathode of the iir'stdischarge device represented by rectangle The output network i3 may beconnected from the anode and cathode of the lastv discharge devicerepresented by the rectangle 1 to the input of any additional stages ofamplification that may be required. v As previously stated, the cameratube is one having extremely high impedance and thus the currentproduced thereby is ,not materially affected by the load impedance intowhich the tube operates. This current, we may consider to be representedby the dotted line A of Fig. 2a and it is desired that this current beamplified with uniform amplification over the frequency band to producea voltage at the output terminals 3 and 4, which voltage may likewise berepresented by a straight line, as indicated by the curve A' of Fig, 2d.l

'Ihis current fiows through the impedance between terminals I and 2.This impedance is made up of the input capacitance of the firstdischarge device represented by rectangle which capacitance is indicatedby dotted lines at I4, in shunt with such impedances as are presentacross the circuit, including, for example, resistance such as thatindicated at I6 and I1 through whichbias voltage may be supplied to thegrid of the first stage of the amplifier 5. Such resistance is necessaryto produce a limiting finite impedance at low frequencies across theinput to the first discharge device of amplifier 5. The voltage acrossthese terminals produced by the camera tube may, by reason of theseimpedances, vary with frequency as indicated, for example, by the curveB of Fig. 2a.

This voltage isas minute as it is practicable to make it and still beamplifable in the presenceof the noise level of the amplifier, the mostobjectionable of the noise currents introduced by the amplifier being atlow frequency, below the line repetition rate, or below two thousandcycles.

Of course, one way to correct for the attenuation at high frequency,represented by the curve B is to connect across the circuit, a seriescombination of inductance and resistance proportioned with respect tocapacity I4 to produce uniform impedance at all frequencies to bearnplied. This, however, is not feasible because such inductance andresistance would have such low values that they would so reduce theinput voltage available for amplification at all freout of the question.my invention, no attempt of the circuit, to effect the Instead, acondenser I5 is employed connected between the terminal 2 and a pointbetween the two resistors I5 and I1, this condenser being soproportioned relative to resistances I 6 and I1 as to produce substanthereactance tial reduction in impedance at the intermediate l frequencieswithout materially affecting the impedance at either the low frequenciesorl the high frequencies. Thus, the .voltage across capacitance I4 maynow, by reason of the presence of condenser I5, be represented by thecurve C of Fig. 2a. 'Ihe attenuation, equal to the difference betweencurves B and C,.may be effected while still maintaining the signalintensity above the noise level at all frequencies.

It will be seen that curve C of Fig-2a lies below curve B to asubstantial extent only in' the intermediate part of the range. At theextreme right end of the curve, corresponding to frequencies betweenabout one megacycle and iive megacycles, where condenser I5 hassubstantially zero reactance, the two curves substantially coincide.

In-this range of frequencies the shape of both curves is determinedprimarily by the capacitance I4, the reactance of which at thesefrequencies is low relative to the resistance of resistor I6. In thisrange of frequencies current flowing between terminals I and 2 flowslargely through capacitance I4.

At frequencies below one megacycle the reactance of condensers I4 and I5bothincrease but since the reactance of capacitance I4 is much greaterthan that of condenser I5 it becomes very high relative to resistance I6while of condenser I5 remains negligible with respect to resistance I 6.This is true at about one hundred and fifty thousand cycles. Since thereactance of condenser I4, at the frequency corresponding to the point Yof curve C, is already large relative to resistance I6, it, at this andlower frequencies, has little-or no effect upon the shape of the curveC. Similarly, since the reactance of condenser I5 is negligible at thefrequency corresponding to the point Y; it has little effect upon theshape of the curvey C at that point Y. The shape of the curve at'thispoint Y is determined by the resistance I6 and, therefore, 'curve C inthe region of point Y is substantially a straight line nearly parallelto the horizontal, or frequency, axis of the graph.

At frequencies below the point Y, the reactance of condenser I5increases and first becomes high relative to resistance I6 and finallybecomes'high as compared with resistance II, which is about ten timesgreater than resistance I6. Thus, the voltage between terminals I and 2rises with reduced frequency until the point X is reached where thereactance of condenser I5 is that it no longer is effective indetermining the shape of the curve. Below this pointX,curves B and Ccoincide.

While the use of condenser I5 results in a loss of signal input over aregion of intermediate frequencies, it does not reduce the signal inputat low frequencies where the noise level is highest. It produces theimportant advantage of dividing the signal frequency band in twodistinct portions each having distinctly different signal levels andwhich may be treated separately. ,Both portions may now be amplifieduntil the lower frequency portion, which is of higher intensity, becomesof such amplitude that further amplification with a given tubecomplement results in distortion due to overloading. The lower frequencyband may then be attenuated to produce uniform amplification over theentire lower frequency portion of the band without loss in amplincationin the higher frequency portion of the band, without changing thecharacteristic relation between voltage and frequency in the highfrequency portion of the band, and without reducing the signal level toa point objectionably close to the noise level at low frequencies.

Now the entire band may be amplified to such a level that circuits maybe employed to increase the intensities of currents of the highestfrequencies in the band to a level of the low frequency currents. Suchcircuits are of such character, as will presently be explained, thatthey produce a loss at all frequencies and especially the lowfrequencies. However, by reason of my invention, such circuits may beemployed after sufiicient amplification has been had that this loss maybe tolerated without reducing the signal to a level too close to thenoise level of the amplifier.

The voltage represented by the curve C is amplified by the amplifier 5and produces a. current represented by the curve. I1 of Fig. 2b at theoutput of the amplifier 5. This curve I1 has thesameshapeasthecurvecofllig.2asincethe amplifier 6 has uniformamplication at all frequencies involved vand its last stage has highinternal impedance to currents in its output circuit as previouslymention This current is supplied by amplifier to the network II couplingthat amplier to the amplifier 6. A portion of this .current flowsthrough resistance I3 and by-pass condenser I3. The voltage on theresistance I6I is supplied through coupling condenser 20 to the grid ofthe first discharge device of the amplifier 6. Between the grid andcathode of this discharge device is connected the series combination ofinductance 2l and resistance 22,- which are proportioned relative to theshunt capacitance 23, effective across the input of the amplier 6 tohave uniform impedance throughout the band to electromotive forceexisting across the combination 2l, 22, and

Connected across 'condenser 2li is a path comprising resistance 24,condenser 25, and resistance 26, the elements I3, 20, 24, 25, 26, 2| and22 being proportioned relative to resistances I6 and I1 and capacitanceI5 4to attenuate the low frequency currents in the band, thereby toproduce voltage across capacitance 23, which voltage may be representedby the curve Ec of Fig. .2b.

This is effected by so proportioning the ele-- ments that the sum ofresistances I6 and 22 bears the same ratio to resistance I6 that the sumof resistances 24 and 26 bears to resistance I1, and that thecapacitance of condenser I5 bears to the capacitance of condenser 20. l,

In the path 24, 25, and 26, the resistances 24 and 26 are of equal valueand the condenser 25 is of negligible reactance as compared with the sumof resistances 24 and 26 at thelowest frequency to be amplified; forexample, ten cycles per second. In other words, the path 24, 25, 26 isessentially purely resistive throughout the band. Resistances 24 and 25are so large that capacity betweencondenser 25 and ground does notmaterially affect the transmission characteristics of the channel.

Such proportioning of the elements not only produces uniformamplification over the lband including frequencies up to 150,000 cycles,but it also renders the system as will later be shown, independent offrequency so that no undesired phase shifts at the different frequenciesare produced.

This network produces attenuation at the lower frequencies amplificationdesired. `This attenuation occurs. however, after the amplification ofamplifier 5 has'been had so that the voltage Es is still above the noiselevel of amplier 6`even at low frequencies where the disturbing currentsare the most intense.

Having produced uniform amplification over the low frequency portion ofthe band: i. e., up to 150,000 cycles, it now remains to accentuate thehigh frequencies sumciently to produce uniform amplication over theentire` band. The band over which accentuation is to be effected and themagnitude of accentuation required is now much less than would be thecase if all of the compensation were to be effected in a single stage ofthe amplifier.

The voltage represented by the curve En is amplified by amplifier 6 inthe presence, of course, of such noise currents as are produced byamplifier 6. 'I'his amplifier supplies to the network l2 an outputcurrent which is represented by the curve In of Fig. 2c. The signalvoltage on resistance 21 is supplied through coupling condenser 30 tothe input of the iirst discharge device of amplifier 1 between the gridand cathode of which is connected a network comprising an inductance 3l,resistance 32, resistance 33 and bias battery 34, a condenser 35 beingconnected between ground and a point between resistances -rightgr endoffthe curves C,

-`by the condenser to bring about the uniform necessary that inductance32 and 33. The resistance 33 may be variable, if desired, to correct forchanging internal resistance in the source 34 which may be a battery.

Resistor 21, which comprises a portion of the network I2 is connected inthe path -through which unidirectional anode current tothe last stage ofamplifier 6 is supplied, and has, therefore, a high resistance. 0nly asmall fraction of the signal currentoutput of the amplifier 6 flowsthrough this resistor, the remainder of the output current flowingthrough condenser 30 and the series parallel combination represented byelements, 32, 33,-34, 35 and 36. That is, the impedance looking to theright of the juncture of resistance 21 and condenser 30 is considerablylower than the resistance 21 over the entire range of frequenciesinvolved. Condenser 30 serves as a blocking condenser to preventapplication of unidirectional anode voltage to the grid of the firststage of amplifier 1. This condenser must have a reactance substantiallylower than the resistance 21 at the lowest frequency considered, i. e.,ten cycles per second, so that the impedance into which amplier 6 worksis determined principally by elements 30, 3l, 32, 33, 34, 35-and 36ofithe network I2.

Since, as has been shown earlier, the 'extreme Ee, and Ie is affectedI4, acting together with resistor I6, the impedance elements 3| and 32are proportioned in such va manner that the time `4constant of theseries combination of elements 3| and 32 is the same 4as the timeconstant of the parallel combination of elements I4 and I6 in order toeilect compensation for the phaseV and amplitude of the currents andvoltages in the upper range of frequencies.

It is important ,that the frequency at which the network I2 resonates benot lower than'2 to 3 times the upper limit of the amplifier system; i.e., from l0 lto l5 megacycles in the embodiment shown, in eilect shallnot affect transmission in the band. This resonance is producedprimarily by inductance 3l and capacitance 36. Since stray capacity 36cannot be reduced appreciably, it is 3l be chosen to resonate with thecapacity 36 at a .frequency Well outside of the pass-band of theamplifier. Thus, the resistance 32 and the inductance 3|, in general,have exceptionally low values when the circuit is adjusted to givenearly exact compensation. For example, the resistance 32 may be tenohms and the inductance 3I three microhenries.

By so proportioning these elements, uniform amplification over theentire band up to the input of amplifierA 1 may be had. Itso happens,however, that since the value of resistance 32 and inductance 3lrequired to produce such uniare very small, they reduce formampliilcation signal over the entire band.

the intensity of the However, at this point of the circuit, the previousorder that the resonance reduced to a pointzinsuiiiciently above thenoise level of ampliner I then resistance 33 and condenser 35 may beincluded in the circuit and proportioned relative to resistance 32 inthe same way that resistance I 'I and condenser I5 are proportionedrelative to resistance i6 thereby to increase the impedance at lowfrequencies to produce a voltage across capacitance 36 varying withfrequency in the manner illustrated by curve E7 of Fig. 2c. Condenser 35is a substantial short circuit to resistance 33 at the high frequenciesto be accentuated but is of suiciently high reactance at the lowfrequencies where noise currents are most objectionable to renderresistance 33 effective in series with resistance 32 to increase theimpedance across the channel and bring about the increased low frequencyamplification evidenced by the left end of curve E1.

This voltage Ev is amplified by amplifier 'I. which produces a currentin its output which may be represented by the curve I7 ofFig. 2d. Thiscurrent is supplied to the network I3 which is identical in its actionto network II. That is, it reduces the low frequency voltage supplied tothe terminals 3 and 4 relative to the high frequency voltagel therebyproducing transformation between current at the terminals I and 2 andvoltage at the terminals 3 and 4 which is uniform at al1 frequencies inthe band of frequencies to be transmitted. This voltage at terminals 3and 4 is represented by the curve A of Fig. 2d and may be of anintensity of the order of half a volt, well above noise level at allfrequencies, and such that it may be readily ampliled to any desiredintensity required for the transmission of the picture representedthereby` by modulation be transmitted by radio.

It will thus be seen that an important feature of my invention residesin the use of the network I5, I6, I'I at the input to amplifier 5.'I'his network, in effect, divides the frequency band into two portions,the low frequency portion below the frequency represented by point Y ofFig. 2a and the high frequency portion above the frequency representedby this point Y. This permits these two portions to be treatedseparately in the respective networks II and I2, the

network IIl producing uniform amplincation over the low frequencyportion of the band with an output intensity above the noise level ofamplifier 6 and the network I2 accentuating voltages in the highfrequency portion of the band. Since, however, the elements required toaccentuate the high frequency currents may reduce the intensity of thelow frequency currents to intensities unsatisfactorily small, theelements 35 and 33 may be included to maintain the lows suiiicientlyabove the noise level of amplifier 1. Network I3 then brings about theuniform amplication over lthe band.

I have now generally set forth the character of my invention. For a moredetailed consideration let us first consider the amplifier 5 and thenetworks between which it operates, and the portion of the band offrequencies below the point Y of Fig. 2a. This point is at a frequencybelow the frequencies `the transmission of which is affected bycapacitance Il and above the-frequencies the transmission of which isaii'ected by condenser I5.

Jn E=1 12m-LJ. R11-T where I represents the current supplied to theinput through terminals I and 2; E represents the voltage betweenterminals I and 2; R and C repupon a carrier wave to p Since the networkII compensates for the variation in transmission with frequency causedby elements I5, I 3, II, it, of course, is designed relative to thatnetwork.

resent, respectively, the resistance and capacity of the elements ofFig. 1 designated by the reference numeral written as a subscript afterthe respective character; w represents frequency multiplied by theconstant 21|- where'1r=3.1416; and 7 represents the imaginary quantity,V11. f

This nomenclature will be employed throughout the following.

Equation 1 is true only for frequencies below the point Y of Fig. 2a; i.e., below around 150,000 cycles. I

If G represents the overall mutual conductance of amplifier 5 then thecurrent I1 at the output of amplifier 5 may be expressed by thefollowing equation:

Now, neglecting the capacitance C23 and letting L21; i. e., thereactance of inductance 2|, equal zero, the impedance Zn of network IIas reviewed from amplier 5 may be expressed as follows:

[ -R24+R26 ]R Substituting from Equation 2 for I1, and from Equation 3for Zn;

Simplifying and substituting from Equation 1 for E:

man: s

If Raz-l-R1a=aRis, where ais a .real constant: Rn4+R2e=aRi1 andC1a=aCao, then from Equation 4 the following is obtained: y

the frequency Y if the above proportionalities be made. i Moreover, allof the quantities in Equation 5 are real quantities, which means thatthere is no phase shift between the current I supplied at terminals Iand 2 and the voltage Ea supplied to amplifier 6 over the frequencyrange below the point Y.

6 and produces current Ie in network l2 where compensation for theeffect of capacitance I4 at high frequencies is made.

Now, considering frequencies higher than that corresponding to point Y,it is necessary, as previously stated, that the time constant of theelements 3l and 32 equal that of the elements IB and Il or that %=Rc Theseries circuitcomprislng inductance 3| and resistance 32. having thesame time constant as' the shunt circuit comprising capacitance Il andresistance I6, produces exactly equal and opposite effects upon thetransmission through the system, and thus, except for theeffect ofelements 35 and 33 at low frequencies, uniform amplincation over theentire band, exists between the terminals I and 2 and the input toamplifier 1.

Elements 35 and 33 may be necessary, however,

in order that the signal voltage be large enough at the low frequenciesto override the low frecase after the 'signals have been transmittedthrough the amplifier`1, the low frequencies may be attenuatedsufficiently to match the high frequencies as indicated by curve A' ofFig.` 2d and thus produce uniform ampliiication over the`55 band uptothe output terminals and signal intensity at the output well above thenoise level of any subsequent amplifiers. c

While in this specication and claims I have referred to wide bandamplifiers and have para0 ticularly mentioned the frequency bandextending from ten cycles to four or five megacycles, it will, ofcourse, be understood that my invention is readily applicable toampliers operating over much narrower bands of frequencies. tion findsutility in any amplifier where the signal level to be amplified and thefrequency range over which the amplifier must operate are such that theattenuating effects of shuntcapacitance cannot be compensated ina-single networkl of 'I9 the amplifier without undesirably reducing the.

- signal level.

While 'I have shown a particular embodiment 'of my invention, it will,of course, be understood My inven- 65 1. In an amplifier for producinguniform ratio between input current and output voltage, said amplierhaving resistance and capacity in shunt with its input to which saidcurrent is supplied, said current having frequencies extending over awide band and having. intensities only slightly above the noise level of'said amplifier, the method which comprises attenuating currents in theintermediate frequency portion of said band above the frequency of themost intense noise currents of the amplifier without changing thecharacteristic relation between intensity of voltage on said resistanceand capacity-and frequency in the high frequency portion of the band,attenuating in a later stage of the amplifier low frequency currents toproduce uniform amplification at all frequencies below said highfrequency l 25 portion of the band and thereafter accentuating Thisvoltage Ee is now amplified by amplifier quency accentuation occursthereby to avoidv overloading said last mentioned stage with currents tobe attenuated.

2. In an amplifier for producing 'uniform ratio between input currentand output voltage, said amplifier having resistance and capacity inshunt with its input to which said current is supplied.

said current having frequencies extending over a wide band, the methodwhich comprises attenuating currents in the intermediate frequencyportion of said band above the frequency of the most intense noisevcurrents of the amplifier without' changing the characteristic relationbetween intensity of voltage on said resistance and capacity andfrequencyin the high frequency portion of vthe band, amplifying theentire band, reducj ing the voltages having frequencies below saidquency noise level ofthe amplifier 1. In that high frequency portion ofthe band to uniform thereafter accentuating the voltages in the highfrequency portion of said band sufficiently to overcome the effec-t ofsaid shunt resistance and' gapacityin said high frequency portion of the3. The combination, in an amplifier for electrol motive forces existingacross a capacitance at the input to said amplifier, said electromotiveforce having frequencies extending over a wide band and having intensityat low frequencies only slightly above the level of undesired lowfrequency currents, of a resistance across said capacity, a portion ofsaid resistance being shunted by a second capacity, 'said portion andsaid second capacity being proportioned to reduce voltage across saidfirst capacity above said low frequencies without affecting thecharacteristic relation between said voltage and frequency at highfrequencies, means between stages -of the amplifier to produce uniformamplification at all frequencies below said \high frequencies V whilemaintaining the voltage above the noise level and means between laterstages of said that I do not wish to be limitedthereto sincel amplifierto accentuate the high frequencies :o

produce uniform amplification at said frequencies.

4.7The combination, in a multistage amplifier, a circuit at the input toone of the stages of said amplifier having shunt resistance and capacityproducing attenuation of high frequency currents in the band to beamplified, a circuit between stages in said amplifier having shuntresistance and capacity, an inductance in series with said lastresistance, said inductance and said resistance having a time constantequal to the time constant of said first mentioned shunt resistance andcapacity, a shunt` combination of resistance and capacitance in serieswith said second mentioned shunt resistance proportioned to reduce theattenuation caused by said inductance and the resistance in series withit of low tween stages in said amplifier having shunt rean inductance inseries resistance, said inductance and said resistance having a timeconstant equal to the time constant of said first mentioned shuntresistance and capacity, a shunt combination of mission of highfrequency currents.

7. In combination, an amplifier channel having shunt resistance andcapacity to which current to be amplified is supplied, said currenthaving such intensities and frequencies extending pling capacity,

form amplification ratio over a band of frequencies intermediate in saidfirst mentioned band, and means, thereafter, to compensate the variationin amplification .of said amplifier with respect to frequency over theportion of said band below said intermediate portion, and a subsequentstage. of said amplifier having means to compensate the variation inamplification over the portion of the band above said intermediatefrequency portion, thereby to produce uniform amplification over theentire band.

8. 'Ihe combination, in a wide band amplifier havingv resistance andcapacity in shunt with the input thereof and additional capacityshunting a portion of said resistance, and having an interstage networkcomprising an interstage coupling capacity shunted bya second resistanceand having shunt resistance at either side of said coupling capacit saidfirst resistance, said portion and said additional capacity beingproportioned to accentuate low frequency current with respect to currentof intermediate frequency in the band to be amplified, and said couplingcapacity, second resistance and shunt resistances being proportionedrelative to said additional capacit said portion and first resistance toattenuate said low frequency currents to produce uniform amplificationat alllow frequencies.

9. The combination, having resistance and capacity in shunt with theinput thereof, and additionalcapacity shunting a portion of saidresistance, and having an interstage network comprising a couplingcapacity shunted by a second resistance and having shunt resistance ateither side of said coupling capacity, the ratio ofthe sum of said shuntresistances to that part of said first resistance not shunted by saidadditional capacity being equal to the ratio of said second resistanceto said portion of said first resistance, and these ratios both beingequal to the ratio of said additional capacity to vsaid series capacity.

10. The combination, in a wide band amplifier having resistance andcapacity in shunt with the input thereof, and additional capacityshunting a portion of said resistance, and having an interstage networkcomprising an interstage coupling capacity shunted by a secondresistance and having shunt resistance at either side of said coutheratio of the sum of said shunt resistances to that part lof said firstresistance not shunted by said additional capacity being equal to theratio of said second resistance to said portion of said first resistanceshunted by said additional capacity, and these ratios both being equalto the ratio .of said additional capacity to said coupling capacity, andan amplifier subsequent to said network amplifying the currents of allfrequencies in said band, said amplication over the entire band.

Il wlfhe method of amplifying currents having frequencies extending overa wide band in a mulhaving input capacity undeating said low frequencycurrents,

in a wide band amplifier frequency currents relative to intermediatefrequency currents, again amplifying the entire band and thenattenuating said low frequency currents to produce uniform amplificationat all frequencies in the band.

12. In a multistage amplier for currents having frequencies extendingover a wide band and having input capacity undesirably attenuating highfrequency currents in said band, means in said input circuit toaccentuate low frequency currents in said band to a level well above thelow frequency noise level of the first stage of saidV amplifier, meansattenuate said low frequency y in said amplifier subsequent to saidthird stage to currents in a part of said amplifier subsequent to saidiirst stage sumciently to permit amplification of the entire band inamplifier without low frequency overloading of said other stage, meansbetween said other stage and a third stage to accentuate both low andhigh frequency currents in said band relative to currents ofintermediate frequency, and means attenuate said low frequency currentsto the level of said high frequency currents thereby to produce uniformamplification over said band.

DONALD E. NORGAARD.

another stage of said

